Fabrication of Crack-Free Photonic Crystal Films on Superhydrophobic Nanopin Surface

Achieving High-Temperature Stable Structural Color through Nanostructuring in Polymer-Derived Ceramics

Structural colors offer a myriad of advantages over conventional pigment-based colors, which often rely on toxic chemical substances that are prone to UV degradation. To take advantage of these benefits in demanding environments, there is growing interest in producing structural colors from ceramics. Polymer-derived ceramics (PDCs) emerge as a compelling choice, presenting two distinct advantages: their enhanced shape ability in their polymeric state associated with impressive temperature resistance once converted to ceramics. This study pioneers the fabrication of noniridescent structural colors from silicon oxycarbide (SiOC) PDC, enabled by the nanostructuring of an inverse photonic glass within the PDC material. This design, a functionally graded material with an inverse photonic glass (FGM-PhG) structure, leverages the innate light-absorbing properties of SiOC, yielding a vivid structural color that maintains its saturation even in white surroundings. This study elucidates the process-structure-properties relationship for the obtained structural colors by investigating each layer of the functionally graded material (FGM) in a stepwise coating deposition process. To further emphasize the exceptional processing flexibility of PDCs, the three-step process is later transferred to an additive manufacturing approach. Finally, the FGM-PhG structural colors are demonstrated to have remarkable thermal stability up to 1000 °C for 100 h, possibly making them the most thermally stable ceramic structural colors to date.

Preparation of polyphenol-structural colored silk fabrics with bright colors

Conventional textile dyeing relies on the use of dyes and pigments, which can cause severe environmental contamination and waste a large amount of water. Structural coloring is one of the effective ways to achieve environmentally friendly coloring of textiles. In this work, three plant polyphenols with the same o-benzenetriol structure (tannic acid (TA), gallic acid (GA), and tea polyphenol (TP)) were selected as raw materials. Three plant polyphenols can quickly form nanofilms at the gas-liquid interface through a Schiff base reaction with polyethyleneimine (PEI) under mildly alkaline conditions, which were deposited to the surface of silk fabric, allowing precise control over the thickness of film by adjusting the time, resulting in various structurally colored silk fabric. This method for creating structural colors is not substrate-specific and enables the quick production of structural colors on various textile substrates. Furthermore, the structural color silk fabric based on plant polyphenol has antibacterial performance. This textile coloring method is simple, cost-effective and environmentally friendly, providing a new approach to eco-friendly textile dyeing.

Preparation of Natural Plant Polyphenol Catechin Film for Structural Coloration of Silk Fabrics

Traditional textile dyeing uses chemical pigments and dyes, which consumes a large amount of water and causes serious environmental pollution. Structural color is an essential means of achieving green dyeing of textiles, and thin-film interference is one of the principles of structural coloring. In the assembly of structural color films, it is necessary to introduce dark materials to suppress light scattering and improve the brightness of the fabric. In this study, the conditions for the generation of nanofilms of catechin (CC) at the gas-liquid interface were successfully investigated. At the same time, environmentally friendly colored silk fabrics were novelly prepared using polycatechin (PCC) structural color films. In addition, it was found that various structural colors were obtained on the surface of silk fabrics by adjusting the time. Meanwhile, the color fastness of the structural colored fabrics was improved by introducing polyvinylpyrrolidone (PVP) to form a strong hydrogen bond between the fabric and catechin. PCC film is uniform and smooth, with a special double-layer structure, and can be attached to the surface of silk fabrics, giving the fabrics special structural colors. Through the thin-film interference formed between the visible light and the PCC film, the silk fabrics obtain bright, controllable, and uniform structural colors. This method is easy to operate and provides a new way of thinking for environmental-protection-oriented coloring of fabrics.

Preparation of Structural Color on Cotton Fabric with High Color Fastness through Multiple Hydrogen Bonds between Polyphenol Hydroxyl and Lactam

Structural coloration is an important way to realize eco-friendly dyeing of textiles. Structural colored cotton fabric was obtained by fabricating a polydopamine (PDA) film on the white cotton fabric at different polymerization reaction times. PDA is prone to generate capillary tension during film formation, which damages the uniformity and interfacial bonding force of the film. Multiple hydrogen bonds will form between the lactam group of polyvinylpyrrolidone (PVP) and the phenolic hydroxyl group of PDA. The introduced hydrogen bonds will effectively enhance the interfacial bond strength and lead to structural color with high color fastness. The surface morphology of double-layer aggregates of the PDA film on structural colored cotton fabric was revealed by scanning electron microscopy. The chemical constitution of the PDA film and PVP was investigated by Fourier transform infrared spectroscopy and X-ray diffraction. The color characteristics of structural colored cotton fabrics were analyzed by UV-vis reflectance spectroscopy and spectrophotometry.

Structural Coloration of Polyester Fabrics with High Colorfastness by Copolymer Photonic Crystals Containing Reactive Epoxy Groups

Structural color as a revolutionary coloration strategy has been proposed to replace the traditional dyeing and printing process. However, the poor colorfastness and easy crack formation of structural colors on textile fabrics restrict their practical application at present. In this study, poly (tert-butyl acrylate-co-glycidyl methacrylate) (P(t-BA-co-GMA)) copolymers containing reactive epoxy groups with different mass ratios of tert-butyl acrylate (t-BA) and glycidyl methacrylate (GMA) were successfully synthesized, which were used to create structural colors on black polyester fabrics. The results showed that P(t-BA-co-GMA) nanospheres could form crack-free structural colors on polyester fabrics, and the colors vary with the mass ratio of t-BA and GMA to obtain five different colors. The different particle sizes of the different P(t-BA-co-GMA) nanospheres with different refractive indexes and the arrangement of short-range ordered and long-range disordered in microstructures may be the reason of different angle-independent structural colors on polyester fabrics. The P(t-BA-co-GMA) nanosphere structural colors on polyester fabrics possess good abrasion and washing colorfastness. This research provides the experimental basis for the development of crack-free amorphous photonic crystal structural color on fabrics with high colorfastness to promote the practical application of structural color in textile coloration.

Armored colloidal photonic crystals for solar evaporation

Colloidal photonic crystals (CPCs) with a highly ordered crystal structure have attracted great attention in displays, colorimetric sensors and solar energy utilization fields. However, the easily cracking microstructure, inferior assembly efficiency and low refractive index contrast result in poor structural colors. Herein, we develop core-shell poly(styrene-acrylic)@polypyrrole (P(St-AA)@PPy) colloidal nanoparticles by the in situ chemical coupling reaction via droplet microfluidic technology. By membrane separation-assisted assembly (MSAA) and electrostatic spraying strategies, the P(St-AA)@PPy colloidal nanoparticles are assembled into the CPC film, which presents high assembly efficiency and saturated angle-independent structural colors, due to the light-absorbing PPy shell and hydrogen-bond interaction between nanoparticles. Benefitting from these outstanding performances, the P(St-AA)@PPy film shows excellent photothermal properties, which can realize a solar vaporization rate of 1.5825 kg m^-2 h^-1, corresponding to a light-to-vapor efficiency of 94.20%, under 1.0 sun solar irradiance conditions. Our findings open a path for the design of functional CPCs and new-generation photothermal applications.

Subcutaneous Energy/Signal Transmission Based on Silk Fibroin Up-Conversion Photonic Amplification

Transmission of energy and signals through human skin is critically important for implantable devices. Because near-infrared (NIR) light can easily penetrate through human skin/tissue, in this study we report on silk fibroin (SF) up-conversion photonic amplifiers (SFUCPAs) integrated into optoelectronic devices, which provide a practical approach for subcutaneous charging and communication via NIR lasers. SFUCPAs achieve a 4 times higher fluorescence than the control, which gives rise to a 47.3 time increase in subcutaneous NIR energy conversion efficiency of a single fibrous dye-sensitized solar cell compared with the control. Moreover, the hybrid printed electrodes exhibited reversible switching to NIR exposure with a response time of ∼1.06/1.63 s for a 3 s ON/OFF switch. Owing to the flexible, biocompatible, and cost-efficient design NIR-driven optoelectronic performance, the SFUCPAs are promising for use in applications of subcutaneous medical electronics for charging, storing information, and controlling implanted devices.

Direct writing of colloidal suspensions onto inclined surfaces: Optimizing dispense volume for homogeneous structures

HYPOTHESIS

A process to fabricate structures on inclined substrates has the potential to yield novel applications for colloidal-based structures. However, for conventional techniques, besides the coffee ring effect (CRE), anisotropic particle deposition along the inclination direction (IE) is expected to occur. We hypothesize that both effects can be inhibited by reducing the dispense volume during printing by direct writing.

EXPERIMENTS

We combined an additive manufacturing technique, namely direct writing, with colloidal assembly (AMCA) for an automated and localized drop-cast of polystyrene and silica suspensions onto inclined surfaces. Herein, we investigated the influence of the substrate tilting angle and the dispense volume on the printing of colloids and the resulting structures' morphology.

FINDINGS

The results demonstrate that a reduction in the dispense volume hinders the CRE and IE for both particles' systems, even though the evaporation mode is different. For polystyrene, the droplets evaporated solely in stick-mode, enabling a "surface capturing effect", while for silica, droplets evaporated in mixed stick-slip mode and a "confinement effect" was observed, which improved uniformity of the deposition. These findings were used to generate a model of the critical droplet radius needed to print homogeneous colloidal-based structures onto inclined substrates.

Photonic Plasticines with Uniform Structural Colors, High Processability, and Self-Healing Properties

Despite the vast variety of colloidal superstructures available in soft matter photonics, it remains challenging to balance the trade-off between their optical microstructures and material processability. By synergizing colloidal photonics and dynamic chemistry, a type of photonic "plasticine" with characteristics of uniform structural colors, high processability, and self-healing is demonstrated. Specifically, a boronate ester bond-based macromonomer is first prepared through complexation between the diols of polyvinyl alcohol and the boronic acid group of 3-(acrylamido) phenylboronic acid in the presence of concentrated silica colloids. Upon photopolymerization, the dynamic photonic plasticine is formed in situ as the result of the crosslinking of the boronate ester bonded networks. The randomly packed colloids inside the plasticine compose the amorphous photonic crystals, giving rise to angle-independent structural colors that would not compromise during subsequent processing steps; the reversible nature of the boronate ester bonds endows the plasticine with self-adaptable and self-healing properties. Further, the plasticine is also compatible with common shaping methods, that is, cutting, molding, and carving, and thus can be facilely processed into 3D structural colored objects, holding great potentials in fields such as bio-encoding, optical filters, anti-counterfeiting, etc.

Robust hydrophobic veova10-based colloidal photonic crystals towards fluorescence enhancement of quantum dots

Hydrophobic photonic crystals (PCs) has been increasingly appreciated as a promising functional material due to their distinct surface characteristic of structural color and hydrophobicity. However, it remains a challenge to fabricate hydrophobic PCs via a one-step process. Inspired by the development of high-performance waterborne coatings, we propose an easy-to-perform and high-efficiency strategy to construct hydrophobic building blocks (diameter of 221, 247, 276 and 305 nm), where the umbelli-form hydrophobic long chain (veova10 C_n > 9) was loaded onto polystyrene (PS) colloidal particles in situ. Taking advantage of the hydrophobic driving force between the colloidal particles, large-scale colloidal photonic crystals (CPCs) film with crack-free morphology was obtained efficiently. The derived CPCs exhibit robust mechanical stability, prominent hydrophobicity and excellent optical properties. In addition, the colloidal latex holds great potential toward PCs coatings on a variety of substrates (glass, plastic and steel) with excellent adhesiveness. Furthermore, we contrive to construct angle-independent structural color films and supraballs, and explore their application in quantum dots (QDs) fluorescence enhancement, which achieved an enhancement effect by more than eight times. From the standpoint of practical applications, we achieved the flexible high-brightness wearable light-emitting diode (LED) displays. This work will lay a foundation for the development of high-efficiency PCs building blocks, and indicate the direction for the meaningful application of CPCs.

Nematic colloids at liquid crystal-air interfaces via photopolymerization

We demonstrate the preparation of colloidal crystals at nematic liquid crystal-air interfaces by simultaneous photopolymerization and assembly. Polymer colloids are produced by polymerization-induced phase separation of 2-hydroxyethyl methacrylate in the non-reactive liquid crystal (LC) 4-cyano-4'-pentylbiphenyl (5CB) using an open-cell setup. Colloids adsorbed to the nematic 5CB-air interface form non-close-packed hexagonal crystals that cover the entire interface area. We examine the mechanism of growth and assembly for the preparation of LC-templated interfacial colloidal superstructures.

Thick Free-Standing Metallic Inverse Opals Enabled by New Insights into the Fracture of Drying Particle Films

Metallic inverse opals are porous materials with enhanced mechanical, chemical, thermal, and photonic properties used to improve the performance of many technologies, such as battery electrodes, photonic devices, and heat exchangers. Cracking in the drying opal templates used to fabricate inverse opals, however, is a major hindrance to the use of these materials for practical and fundamental studies. In this work, we conduct desiccation experiments on polystyrene particle opals self-assembled on indium-tin oxide coated substrates to study their fracture mechanisms, which we describe using an energy-conservation fracture model. The model incorporates film yielding, particle order, and interfacial friction to explain several experimental observations, including thickness-dependent crack spacings, cracking stresses, and order-dependent crack behavior. Guided by this model, we are the first to fabricate 120 μm thick free-standing metallic inverse opals, which are 4 times thicker than previously reported non-free-standing metallic inverse opals. Moreover, by controlling cracks, we achieve a crack-free single-crystal domain up to 1.35 mm², the largest ever reported in metallic inverse opals. This work improves our understanding of fracture mechanics in drying particle films, provides guidelines to reduce crack formation in opal templates, and enables the fabrication of free-standing large-area single-crystal inverse opals.

Separation-cooperated assembly of liquid photonic crystals from polydisperse particles

Easy and cost-effective production of high-quality photonic crystals (PCs) remains challenging but attractive, not just because they are a type of gemstone but more for their scientific applications (e.g., serving as lossless waveguides, visual sensors, novel pigments and novel separation media). Herein presented is a separation-cooperated assembly (SCA) strategy able to organize cheap polydisperse particles into PCs. Its feasibility was validated through sink-induced SCA of poorly disperse (size variation up to 56%) particles into iridescent liquid PCs in 3 days or more. Strikingly, with a sharp photonic band gap down to 10 nm (ca. 1/7 of the reported 66 nm), the liquid PCs are able to cyclically recover their iridescent color in ca 20 s after agitation, and keep their structural order after dryness, making them practicable to write and paint directly. Also significant is that SCA yielded uniform particles with size variation down to 0.7%. It is thus an easy way to isolate homogeneous particles from disperse ones.